Psychophysics and Neuroscience Foundations

Psychophysics and Neuroscience Foundations

• Distal stimuli are the actual objects or events in the world.
• Proximal stimuli are the physical phenomena produced by distal stimuli that interact with sensory receptors.
• Absolute threshold is the minimum intensity of a stimulus needed for detection.
• Difference threshold (JND) is the smallest detectable difference between two stimuli.
• Top-down processing is influenced by prior knowledge and expectations.
• Bottom-up processing relies solely on sensory input.
• The brain interprets sensory signals based on which neurons are activated, not the stimulus itself (law of specific nerve energies).
• Perception arises from the combined activity of specialized neurons, each responding to specific features (neuron doctrine).

Dendrites and Axons

• Dendrites receive signals from other neurons.
• Axons transmit signals from one neuron to another.
• The typical resting membrane potential of a neuron in the brain is -70 mV.
• Potassium (K+) is more concentrated inside a neuron, while sodium (Na+) and calcium (Ca²+) are more concentrated outside.
• EPSP (excitatory postsynaptic potential) increases the likelihood of an action potential in the postsynaptic neuron (depolarizing event).
• Voltage-gated ion channels open or close based on membrane potential changes, important for action potential generation and propagation.

Light and the Eyes

• A photon is a particle of light that interacts with photoreceptors in the retina, initiating vision.
• Photons trigger chemical changes in photoreceptors, initiating neural signals.
• The human eye perceives electromagnetic radiation with wavelengths between approximately 400-700 nanometers.
• The lens changes shape to focus light on the retina for objects at different distances.
• A strong lens has a short focal length and refracts light sharply, suitable for close objects.
• A weak lens has a longer focal length and refracts light less sharply, suitable for distant objects.
• Cones are densely packed in the fovea.
• Rods are densely packed in the periphery of the retina and are more active in low-light conditions.
• Sensory receptors convert proximal stimuli into neural signals through transduction.

Visual Processing: Ganglion Cells

• On-center RGCs increase firing when light hits the center of their receptive field.
• Off-center RGCs decrease firing when light hits the center of their receptive field.
• Simultaneous light in the center and surround of an RGC's receptive field can neutralize the response.
• Retinal ganglion cells send action potentials to the brain.
• Retinotopic mapping is the spatial arrangement of neurons in the brain corresponding to the retina's layout.
• Mach bands demonstrate how perceived intensity contrasts are exaggerated at edges, differing from the actual physical intensity.

The Visual Brain

• The lateral geniculate nucleus (LGN) relays visual information from the retina to the primary visual cortex.
• Population coding represents sensory information through the combined activity of multiple neurons.
• The ventral pathway (what pathway) processes object identity (color and shape).
• Parasol RGCs → magnocellular layer
• Midget RGCs → parvocellular layer
• Bistratified RGCs → koniocellular layer
• MT area neurons respond best to motion stimuli.
• Simple cells in the visual cortex respond to specific orientations of bars of light.
• A bar of light at a specific angle maximizes the firing rate of simple cells.
• Magnocellular layers process motion and flicker.
• Parvocellular layers process object features like color and form.
• Koniocellular layers respond primarily to color information.

Object Recognition

• Fusiform face area (FFA) is involved in facial recognition.
• Prosopagnosia (visual agnosia) results from damage to the FFA and causes difficulty recognizing faces.
• The parahippocampal place area (PPA) recognizes places, scenes, and spatial layouts.
• Topographic agnosia (place blindness) results from damage to the PPA, making it hard to recognize familiar places.
• Deficits from PPA damage include navigation difficulties and scene perception problems.

Figure-Ground Organization and Perceptual Grouping

• Figure-ground organization is the process by which the visual system separates an image into figure and ground.
• Symmetry influences figure-ground organization; symmetrical shapes are more likely to be perceived as figures.
• Convex borders are more likely to be perceived as part of the figure than concave borders.
• Clutter, variable views, and object variety are challenges for object recognition.
• Gestalt principles of perceptual grouping include proximity, similarity, and common motion.
• Perceptual interpolation fills in missing edges or surfaces.
• Davenport and Potter's study demonstrated that contextual consistency between objects improved recognition speed and accuracy.